1. Field of the Invention
This invention relates to a process for recovering protein from an animal muscle source with improved functional properties and to the protein product so-obtained. More particularly, this invention relates to a process for recovering muscle proteins with improved functional properties from an animal source and the protein product so-obtained.
2. Description of Prior Art
Presently, there is an interest in expanding the use of muscle proteins as food because of their functional and nutritional properties. Better use of these materials would be particularly important with aged or frozen raw materials which are less valuable because they have lost protein functionality. It is presently believed that the muscle tissue utilized as the feed in present processes must be fresh rather than frozen or aged. It is common commercial practice to process freshly caught fish at sea on board ship rather than subject the fish to the time of transportation or the freezing necessary to effect processing on land. Ageing or freezing of fish lowers the functional qualities of the tissue proteins. Protein functionalities of most concern to food scientists are solubility, water holding capacity, gelation, fat binding ability, foam stabilization and emulsification properties.
Protein concentrates from muscle tissue, especially fish, have been made by hydrolysis. This approach has improved some functional properties, particularly solubility, which has allowed its use in prepared soups. However, this approach also destroys other functional properties such as gelling ability.
One process that has had some success in stabilizing protein foods has been the process for producing “surimi”. This conventional process has been used primarily for fish, although there have been some attempts to produce a surimi-like product from other raw materials such as mechanically deboned poultry mince. In producing surimi, the fresh muscle is ground and washed with a variable amount of water a variable number of times. This is determined by the location of the plant and the product that is desired from the particular species. Water may be used in a ratio as low as about 2 parts water to one part fish up to about 5 parts water per 1 part fish; typically about 3 parts water are used per 1 part fish. The number of washes can vary, generally, from 2 to 5, again depending on the raw material, the product desired; and water availability. Twenty to thirty per cent of the fish muscle proteins are solubilized when the ground muscle is washed with water. These soluble proteins, known as sarcoplasmic proteins, are generally not recovered from the wash water of the process. This loss is undesirable since sarcoplasmic proteins are useful as food. The washed minced product containing the protein in solid form then is used to make protein gels. Originally, this was used to produce “kamaboko” in Japan. Kamaboko is a popular fish sausage in which the washed minced fish is heated until it gels. It is presently believed that it is necessary to add cryprotectants to the washed, minced fish before freezing to prevent protein denaturation. A typical cryoprotectant mixture comprises about 4% sucrose, about 4% sorbitol and about 0.2% sodium tripolyphosphate. These components retard the denaturation of the protein during freezing, frozen storage and thawing. It has been proposed by Cuq et al, Journal of Food Science, pgs. 1369-1374 (1995) to provide edible packaging film based upon fish myofibrillar proteins. In the process for making the films, the protein of water-washed fish mince is solubilized in an aqueous acetic acid solution at pH 3.0 to a final concentration of 2% protein. No attempt was made in this work to re-adjust the pH values of the acidified proteins to re-establish the functional properties attained at pH values above about 5.5. In addition, the use of acetic acid imparts a strong odor to the material which would severely limit its use in a food product.
It also has been proposed by Shahidi and Onodenalore, Food Chemistry, 53 (1995) 51-54 to subject deboned, whole capelin to washing in water followed by washing in 0.5% sodium chloride, followed by washing-in sodium bicarbonate. The series of washes, including that using sodium bicarbonate, would remove greater than 50% of the muscle proteins. Essentially all of the sarcoplasmic proteins would be removed. Final residue was further washed to remove residual bicarbonate. The washed meat was then suspended in cold water and heated at 70° C. for 15 min. This heat treatment is sufficient to “cook” the fish proteins, thus denaturing them and reducing or eliminating their functional properties. No attempt was made to restore proteins to improve the functional properties of the capelin proteins.
Shahidi and Venugopal, Journal of Agricultural and Food Chemistry 42 (1994) 1440-1448 disclose a process for subjecting Atlantic herring to washing in water followed by washing with aqueous sodium bicarbonate. Again, this process will remove greater than 50% of the muscle proteins, including the sarcoplasmic proteins. The washed meat was homogenized and the pH varied between 3.5 and 4.0 with acetic acid. In addition, there is an unacceptable odor problem with the volatile acetic acid.
Venugopal and Shahidi, Journal of Food Science, 59, 2 (1994) 265-268, 276 also disclose a similar process for treating minced Atlantic mackerel. The material is washed sequentially with water, bicarbonate solution and again water. The pH is brought to pH 3.5 with acetic acid after homogenization. The proteins were precipitated at pH values greater than 4 on heating the material to 100° C. for 15 min. It is disclosed that “dissolution of structural proteins of fish muscle requires extractants with an ionic strength >0.3”.
Shahidi and Venugopal, Meat Focus International, October 1993, pgs 443-445 disclose a process for forming homogenized herring, mackerel dispersions or capelin dispersions in aqueous liquids having a pH as low as about 3.0. It is reported that acetic acid reduces the viscosity of herring dispersions, increases viscosity of mackerel to form a gel and precipitates capelin. All of these preparations were initially washed with water and sodium bicarbonate, which would remove a substantial proportion of the protein, including the sarcoplasmic proteins.
Chawla et al, Journal of Food science, Vol. 61, No. 2, pgs 362-366, 1996 discloses a process for treating minced threadfin bream muscle after it has been washed twice with water and recovered by filtration. The minced fish product is mixed with tartaric, lactic, acetic or citric acid, is allowed to set and then is heated in a boiling water bath for twenty minutes and then cooled to form a gel. This heat treatment is sufficient to denature the proteins. The washing steps undesirably remove soluble sarcoplasmic proteins from the mince. It is also disclosed that unwashed mince failed to provide the desired gel forming property of surimi.
Onodenalore et al, Journal of Aquatic Food Products Technology, Vol. 5(4), pages 43-59 discloses that minced shark muscle is a source of acidified protein compositions. The minced product is washed sequentially with aqueous sodium chloride, aqueous sodium bicarbonate and then water to remove metabolic substances. This washing effects undesirable removal of sarcoplasmic proteins. The minced product is recovered by filtration. The minced product then is acidified to pH 3.5 with acetic acid, heated in a boiling water bath, cooled and centrifuged to recover a supernatant. The supernatant pH was adjusted to a pH 4-10 using NaOH, heated in a boiling water bath, cooked and centrifuged to recover a second supernatant. Heating the protein dispersion comprising the minced product resulted in 87-94% of the protein remaining in solution while heating of the unacidified protein dispersion resulted in protein coagulation. However, the heating causes protein denaturation. Accordingly, it would be desirable to provide a process for recovering a high proportion of available muscle protein from an animal source including a frozen or aged animal source, rather than requiring a fresh muscle tissue source. It would also be desirable to provide such a process, which permits the use of muscle protein sources which are presently under-utilized as a food source such as frozen-or aged fish. Furthermore, it would be desirable to provide such a process which recovers substantially all of the protein content of the process feed material. In addition, it would be desirable to provide such a process which produces a stable, functional, protein product which is particularly useful for human consumption. Such a process would permit its operation at will rather than require initiation of the process very shortly after the animal source is killed so that processing can be extended over a desired time schedule.